1. Field of the Invention
The present invention relates to the field of biotechnology, and especially to viral nucleic acids and cells containing viral nucleic acids. More particularly, the present invention relates to viral nucleic acid sequences that can be part of triplex DNA structures as well as nucleic acid vectors, viruses, and cells containing these viral nucleic acid sequences. It further relates to methods of using such DNA structures and nucleic acid sequences.
2. Description of Related Art
Gene transfer in hematopoietic stem cells (HSC) has great potential, both for gene therapy of inherited as well as acquired diseases, and for the understanding of mechanisms regulating normal and pathological hematopoiesis. As HSC have extensive proliferative capacities, stable gene transfer should include genomic integration of the transgene. Retroviruses based on Moloney murine leukemia virus (MoMLV) have been very popular because they integrate into the host cell genomes and can allow long-term transgene expression. However, these oncoretroviruses do not integrate in non-dividing cells, and most HSC are quiescent. Many pre-stimulation protocols using different cytokine associations have been developed to trigger cycling of HSC in order to render them transducible by oncovirus-derived, mitosis-dependant gene transfer vectors. However, cytokine stimulation induces differentiation together with proliferation and potentialities of HSC could be lost during the transduction process. This problem can be overcome by using lentivirus-derived vectors since lentiviruses have been shown to infect both dividing and non-dividing cells (Poznansky et al., 1991; Naldini et al. , 1996). Initial reports published in the last three years using such lentivirus-derived vectors for transduction of HSC showed promising but very heterogenous results (Case et al., 1999; Evans et al., 1999; Uchida et al., 1998; Miyoshi et al., 1999).
Lentiviruses have evolved a nuclear import strategy which allows their DNA genome to cross the nuclear membrane of a host cell. This active nuclear import of lentiviruses accounts for their unique capacity, among retroviruses, to replicate efficiently in non-dividing target cells, such as tissue macrophages. The restriction of replication of oncoviruses like MoMLV to dividing cells appears to be due to the requirement for disruption of the nuclear membrane barrier during mitosis, allowing MoMLV pre-integration complexes (PICs) to enter the nucleus (Roe et al., 1993). Mitosis-independent replication of lentiviruses, at the origin of their in vivo replication strategy and hence of their pathogenicity, has also enabled the generation of lentiviral gene transfer vectors with promising therapeutic applications (Poznansky et al., 1991; Naldini et al., 1996).
The mitosis-independent replication of lentiviruses was first demonstrated by the productive infection of non-mitotic chondroid cells by the VISNA lentivirus (Thormar, 1963). Soon after its discovery, HIV was shown to replicate in differentiated primary macrophages (Gartner et al., 1986; Ho et al., 1986). HIV DNA integrates in the chromatin of non-mitotic target cells (Weinberg et al., 1991; Lewis et al., 1992), implying that HIV-1 PICs are able to cross the nuclear membrane of host cells (Bukrinsky et al., 1992). Thus, mitosis-independent nuclear import is a pivotal event responsible for the ability of lentiviruses to replicate in non-dividing cells.
The search for the viral determinants responsible for the active nuclear import of the HIV-1 DNA genome has constituted an active but controversial field of investigation. The presence of putative nuclear localization signals (NLSs) within the matrix (MA) and Vpr viral proteins has led to the proposition that they could act in a redundant manner in HIV-1 DNA nuclear import (Bukrinsky et al., 1993b; Emerman et al., 1994; Popov et al., 1998; von Schwedler et al., 1994). It has been proposed that phosphorylation of a small subset (1%) of MA molecules at a C-terminal tyrosine residue triggers their release from the plasma membrane and their association with HIV-1 integrase protein (Gallay et al., 1995a; 1995b). The contribution of these proteins to the karyophilic properties of HIV-1 PICs is currently a matter of strong debate (Freed and Martin, 1994; Freed et al., 1995; Fouchier et al., 1997; Freed et al., 1997; Koostra and Schuitemaker, 1999). More recently, NLS motifs have been identified in the integrase protein (IN) and mutations in these motifs have been reported to abolish the interaction of IN with karyopherin α, a cellular NLS receptor (Gallay et al., 1997).